TIANJIN: Huge explosions in a warehouse district sent up massive fireballs that turned the night sky into day, killing at least 44 people and injuring hundreds in the Chinese port city of Tianjin, officials and witnesses said Thursday.

Twelve of the dead were from among the more than 1,000 firefighters sent to fight the blaze set off by the explosions shortly before midnight, the official Xinhua News agency said. It said 520 people were being treated in hospitals, 66 of them with serious injuries.

The blasts, originating at a warehouse for hazardous material, turned buildings in the immediate vicinity into charred, skeletal shells while shattering windows up to several kilometers (miles) away.

"I thought it was an earthquake, so I rushed downstairs without my shoes on," said Tianjin resident Zhang Siyu, whose home is several kilometers from the blast site. "Only once I was outside did I realize it was an explosion. There was the huge fireball in the sky with thick clouds. Everybody could see it."

Zhang said she could see wounded people weeping. She said she did not see anyone who had been killed, but "I could feel death."

There was no indication of what caused the blasts, and no immediate sign of any large release of toxic chemicals into the air. Beijing News said there was some unidentified yellow foam on the ground at the site, although it was not clear if this was contamination or part of the fire-fighting efforts.

"It was like what we were told a nuclear bomb would be like," said truck driver Zhao Zhencheng, who spent the night in the cab of his truck after the blasts. "I've never even thought I'd see such a thing. It was terrifying, but also beautiful."

Police in Tianjin said an initial blast took place at shipping containers in a warehouse for hazardous materials owned by Ruihai Logistics, a company that says it is properly approved to handle such materials. State media said senior management of the company had been detained by authorities, and that President Xi Jinping has demanded severe punishment for anyone found responsible for the explosions.

Xinhua said an initial explosion triggered other blasts. The National Earthquake Bureau reported two major blasts before midnight, the first with an equivalent of 3 tons of TNT, and the second with the equivalent of 21 tons.

The explosions took place in a mostly industrial economic development zone, with some apartment buildings in the vicinity. Buildings of a half-dozen other logistics companies were destroyed in the blasts, and more than 1,000 new cars were left charred in a nearby parking lot, the Beijing News said.

The Tianjin municipality said more than 1,000 firefighters were sent to fight the ensuing fire, which was mostly under control by morning.

As is customary during disasters, Chinese authorities tried to keep a tight control over information. Police kept journalists and bystanders away with a cordon about 1 or 2 kilometers (about a mile) from the site. On China's popular microblogging platform of Weibo, some users complained that their posts about the blasts were deleted, and the number of searchable posts on the disaster fluctuated, in a sign that authorities were manipulating or placing limits on the number of posts.

The website of the logistics company became inaccessible Thursday.

The Tianjin government said that because of the blasts it had suspended online access to public corporate records. These records might be used to trace the ownership of Ruihai. It was not clear whether the blackout was due to technical damage related to the explosion. No one answered the phone at the Tianjin Market and Quality Supervision Administration or the Tianjin Administration for Industry and Commerce Thursday.

Ruihai Logistics said on its website — before it was shut down — that it was established in 2011 and is an approved company for handling hazardous materials. It said it handles 1 million tons of cargo annually.

Photos taken by bystanders and circulating on microblogs show a gigantic fireball high in the sky, with a mushroom-cloud. Other photos on state media outlets showed a sea of fire that painted the night sky bright orange, with tall plumes of smoke.

About 2 kilometers (1.2 miles) from the explosion site is the luxury Fifth Avenue apartment complex on a road strewn with broken glass and pieces of charred metal thrown from explosion. Like surrounding buildings, the Mediterranean style complex had all its windows blown out, and some of its surfaces were scorched.

"It's lucky no one had moved in," said a worker on the site, Liu Junwei, 29. "But for us it's a total loss. Two years of hard work down the drain."

"It had been all quiet, then the sky just lit up brighter than day and it looked like a fireworks show," said another worker on the site who gave just his surname, Li.

Tianjin, with a population of about 15 million, is about 120 kilometers (75 miles) east of Beijing on the Bohai Sea and is one of the country's major ports. It is one of China's more modern cities and is connected to the capital by a high speed rail line.--AFP